If the markings are distinct enough and the weapon is an automatic, and the right equipment is used any one of the following can be used to match a gun to a spent bullet or cartridge case; rifling from the barrel, breech face impressions on the the case bottom, firing pin mark on the primer, extactor marks on the case rim, chamber marks on the case, ejector mark or indentation on case bottom, magazine lip marks on the case as it slides off the follower (you can determine which marks were made by the feed lips when loading and which were made when chambering). This in addition to burned and unburned powder in the gun matching that on the base of bullet or in the spent casing, especially if it precisely matches any other unfired ammo you had laying around. Sabots eliminate rifling marks only if you find the spent sabot before the investigators do. A quicker solution, if you think you might have to compromise a auto-pistol, in what is in your mind a justifiable shooting, is to immediately after purchase, obtain a complete replacement upper and ejector and use it for carry, but always use the original for practice so that the amount of wear on both components match. If compromised, the new compromised upper is removed, then destroyed, and the old original upper is put back on. The throw a way upper must be purchased cash, piece by piece. Get rid of any remaining ammo of the same lot and even brand, including the range brass you picked up. Need to destroy the offending magazine also, no matter how much you paid for that hi-cap bugger. Keep in mind that all of this is super duper illegal. Not reporting a shooting, obstruction of justice, suspicion of murder, maybe even suspicion of pre-mediated murder, etc. etc.... If the shooting is high profile enough and the the FBI labs are brought in, you would be amazed at what they can find. If some gang banger tries to rob you and you draw that bad boy and light him up, ensure there were no wittness that give a crap and then walk away, the cops are going to figure it was drug or gang related. If you are caught later, even though it would be bad, an argument could be made that you fled and never told authorities because you were afraid of retaliation from his fellow gang members, cousins, brothers, father, etc... These could be real concerns. All of the above posting is for information only and not intended as advice, legal or otherwise, or as encouragement to do anything illegal.
[This message has been edited by TEX (edited September 29, 1999).]